Distributed automation systems are often applied in automation technology (manufacturing automation, or process automation) for plant control. Serving for registering and/or influencing the process variables relevant for the control are so-called field devices. Examples therefor include fill level measuring devices, mass flow measuring devices, pressure and temperature measuring devices, etc., which, as sensors, register the corresponding process variables fill level, flow, pressure, or temperature.
Serving for influencing process variables are actuators, e.g. valves or pumps, via which the flow of a liquid in a pipeline section, or the fill level in a container, can be altered.
A large number of such field devices are available from the members of the firm, Endress+Hauser.
For data exchange between the field devices and superordinated units (e.g. control systems, control units, etc.), fieldbus systems are applied. The superordinated units serve for process control, process visualizing, process monitoring and plant monitoring, as well as for start-up and for servicing the field devices.
Also referred to as field devices are, generally, units, which are connected directly to a fieldbus and serve for communication with superordinated units (e.g. I/Os, gateways, linking devices, controllers). Frequently, fieldbusses are also integrated in enterprise networks, which work on an Ethernet basis, in order that process, or field device, information can be accessed from different regions of an enterprise.
For global communication, company networks can be connected with public networks (e.g. Internet).
For servicing and for start-up of the field devices, corresponding operating programs are necessary (e.g. FieldCare of Endress+Hauser; Pactware; AMS of Emerson; Simatic PDM of Siemens).
Serving for plant control of larger plants are control system applications (e.g. Simatic PCS7 of Siemens; Freelance of ABB; Delta V of Emerson).
An essential aspect of open fieldbus systems (Profibus, Foundation Fieldbus) is the interoperability and exchangeability of devices of different manufacturers. In a plant, devices (sensors, actuators, etc.) of different manufacturers can be applied together. In the case of failure of a sensor of a particular manufacturer, an option is to substitute for such a similar sensor of another manufacturer.
These requirements necessitate a clear structuring of data and functions in the individual field devices, in order to enable unified accessing. This is achieved through a standardized block model, which underlies both of the fieldbus systems, Profibus and Foundation Fieldbus.
Data and functions of a field device are, in such case, encapsulated in different blocks, which appear externally as communication objects. Each field device working according to the block model includes at least one device block (resource block), which provides all data identifying a device, e.g. device manufacturer name, serial number, hardware, and company, versions, etc. In addition to the device block, there is a transducer block, which serves for conditioning signals. As a rule, the signals are raw signals (input signals), which come from a measuring transducer and must be conditioned, before they can be fed to additional function blocks. In the transducer block, there occurs a calibrating and a linearizing of the raw signal, so that the actual measured value is available as output signal of the transducer block. A large number of predefined, basic function blocks are made available. Typical function blocks are: Analog input, analog output, digital input, digital output, PID controller, etc. These function blocks are combined to form a control strategy in the field devices with the assistance of a corresponding operating tool, e.g. ControlCare of the firm, Endress+Hauser. The so created control strategy serves exclusively for the process control.
Serving for plant monitoring (asset management) are, as a rule, corresponding application programs, which likewise run on the superordinated units.
Process control and plant monitoring are, most often, two completely separate systems. Data exchange between these systems is only implemented with considerable effort.